Electrical circuitry often must be protected from disruptions caused by electromagnetic interference (EMI) and radio frequency interference (RFI) entering the system. EMI energy can be generated outside of as well as inside the system and can occur anywhere in the electromagnetic spectrum. External EMI energy is an undesired conducted or radiated electrical disturbance that can interfere with the operation of electronic equipment, while internal EMI energy is the unwanted noise or unwanted interference generated by electrical or electronic circuitry within a system.
RFI is now used interchangeably with EMI but generally is limited to interference in the radio communication band. Connectors are particularly susceptible to EMI energy because of the numerous contact areas and openings for cable and external electrical contacts. The art, however, has developed sophisticated electrical connectors having substantial shielding effectiveness against EMI/RFI energy.
Often it is also desirable to have shielded cable as well as shielded connectors. In conventional flat cable applications where shielding is necessary, ribbon cable has been employed. These conventional ribbon cables may employ a metallic shield such as aluminum foil surrounded by a taped insulating jacket of polyester or the like. Other shielded ribbon cable is compressed of copper braid embedded in the insulation. An additional method of providing a sheilded cable for ribbon cable is to employ a copper braid surrounding the cable.
Although the concept of employing an aluminum foil in a polyester jacket for ribbon cable can be extended to shield flat flexible cable, flat cable shielded in this manner is significantly less flexible than unshielded flat cable and is, therefore, unsuitable for those applications where a high degree of flexibility is required.
Similarly, a copper braid can be used to form a shield surrounding flat flexible cable which can in turn be encapsulated than a polyester jacket. This form of shielded flat flexible cable, however, is even less flexible in the aluminum foil configuration. In addition to the reduction in flexibility imposed by these methods of shielding, these are fairly expensive to manufacture.
It is an object of the present invention to provide a shielded flat flexible cable that protects against EMI and RFI.
It is a further object of the invention to provide a shielded flat cable that retains the inherent flexibility of unshielded cable. In addition, it is an object of the invention to provide a shielded flat cable that is cost effective to manufacture.